The present invention relates to a measuring device for measuring a distance between a reference mark and a target object.
Measuring devices for laser distance measuring systems are made up of an electro-optical component designed as a beam source, a further electro-optical component designed as a detector, transmitting optics and receiving optics. The beam source and the transmitting optics are designated as the transmitting device and the detector and the receiving optics as the receiving device. The beam source emits a laser beam along an optical axis. The laser beam is focused by the transmitting optics and aimed at the target object. A reception beam reflected and/or scattered by the target object is shaped by the receiving optics and aimed at the detector along an optical axis. Measuring devices are divided into paraaxial arrangements in which the optical axes of the transmitting and receiving devices run in a parallelly offset manner, and coaxial arrangements in which the optical axes of the transmitting and receiving devices are stacked on top of one another and separated with the aid of a beam-splitting optical element. In the case of coaxial arrangements, the transmitting optics and the receiving optics are integrated into a common beam-shaping optical element, which shapes the laser beam and the reception beam.
European Patent Document No. EP 1 351 070 A1 discloses a known measuring device having a paraaxial arrangement of the transmitting and receiving devices. The beam source, the transmitting optics and the receiving optics are fastened on an optics carrier that is rigid per se. The detector is fastened on a printed circuit board, which is mechanically rigidly connected to the optics carrier via a screwed connection. The beam source and the receiving optics are inserted to their full extent into receptacles in the optics carrier and, where applicable, fixed with an adhesive connection in the optics carrier. The transmitting optics are adjustable along the optical axis thereof in the optics carrier and are adjusted when the beam source is activated; the optics are adhered to the optics carrier in the adjusted position. With an activated beam source, a manipulator is used to displace the detector relative to the printed circuit board in all three spatial directions, i.e., in the direction of its optical axis and in the plane perpendicular to the optical axis until the reception beam strikes a predetermined region of the detector. Then the detector is fixed in the adjusted position on the printed circuit board with a soldered connection. Adjustment tolerances are equalized by adjustment gaps with solder bridges and enlarged contact surfaces.
The disadvantage of solder bridges between the printed circuit board and an electro-optical component is that the reliability of the mechanical fastening of the electro-optical component on the printed circuit board is reduced as compared to a soldered connection without a gap. In addition, cold soldered joints may develop in the soldered connection. In the case of a cold soldered joint there is no integral connection between the solder and the connection partners. The mechanical and electrical properties of a cold soldered joint are deficient. However, cold soldered joints frequently do not cause an immediate electrical interruption. Because cold soldered joints are only able to withstand low mechanical stress, even slight vibrations and shocks to the soldered joint or an elongation of the soldered connection in the event of components that heat up may produce an electrical interruption. In addition to the problems related to production during soldering, solder bridges also have a detrimental effect on the high-frequency properties of the measuring devices. A solder bridge forms an inductivity, which impairs the signal integrity and electromagnetic compatibility (EMC) of the measuring device.
Improving a measuring device with respect to the disadvantages described above would be desirable. The object of the present invention is providing a measuring device for a laser distance measuring system that has a high degree of reliability of the mechanical fastening of the electro-optical components and improved high-frequency properties.
The invention provides that during the adjustment of the measuring device, the first of the electro-optical components arranged in the optics carrier and at least one beam-shaping optical element are adjustable relative to the optics carrier in the direction of the associated optical axes and the second of the electro-optical components arranged on the printed circuit board is adjustable and fixable in the adjusted position in a plane essentially perpendicular to the optical axis of the laser beam or reception beam, which is allocated to the second of the electro-optical components.
An electro-optical component is an optical component which must be supplied with electrical current to operate and which converts electrical current into light or light into electrical current, such as, for example, a beam source or a detector. Designated as an associated optical axis of an optical or electro-optical component is the optical axis of a laser beam or a reception beam, which is allocated to the respective optical or electro-optical component. For example, the associated optical axis of a beam source is the optical axis of the laser beam emitted by the beam source and the associated optical axis of a detector is the optical axis of the reception beam striking the detector.
Because both the first of the electro-optical components and at least one beam-shaping optical element are adjustable during the adjustment of the measuring device in the direction of the associated optical axes, the printed circuit board is able to serve as the locating surface for the second of the electro-optical components arranged on the printed circuit board. The adjustment in the direction of the optical axes is carried out exclusively via the optical and electro-optical components arranged in the optics carrier. The required adjustment of the second of the electro-optical components in the plane perpendicular to the optical axis is carried out via an adjustment of the second of the electro-optical components or via an adjustment of the printed circuit board. Because the printed circuit board serves as the locating surface for the second of the electro-optical components during the adjustment of the measuring device, no gap develops between the printed circuit board and the second of the electro-optical components which must be bridged by a solder bridge.
The plane in which the second of the electro-optical components is adjustable runs essentially perpendicular to the associated optical axis. A slight deviation from the right angle is tolerable as long as the resulting change in spacing from the beam-shaping optical element does not exceed a permissible value. An adjustment path of 500 μm in the plane perpendicular to the reception beam (detector as the second of the electro-optical components) and an angular deviation of 1° produce for example a change in spacing from the beam-shaping optical element of approx. 10 μm. This change in spacing leads to a displacement in the focal position, which is undesirable during the adjustment of the measuring device. The angular deviation may only lie in the order of magnitude in which the resulting displacement of the focal position during adjustment of the measuring device is still permissible. The optical and electro-optical components arranged in the optics carrier are adjustable in the direction of the respective associated optical axes, i.e., the adjustment directions of the components run essentially parallel to the optical axes. Deviations from the parallelism that develop for example because of fabrication tolerances of the optics carrier are permissible.
A preferred embodiment provides that during the adjustment of the measuring device, the printed circuit board is adjustable relative to the optics carrier in the plane perpendicular to the associated optical axis of the second of the electro-optical components and the first contact surface of the optics carrier acts as a locating surface for the printed circuit board in the direction of the associated optical axis of the second of the electro-optical components. The second of the electro-optical components arranged on the printed circuit board is especially preferably designed to not be adjustable relative to the printed circuit board. The advantage of this design is that the electro-optical component arranged on the printed circuit board may already be integrally connected to the printed circuit board prior to adjustment during assembly of the printed circuit board using a soldered connection. In this way, a gap between the printed circuit board and the electro-optical component that would have to be bridged by a solder bridge is avoided. The fact that the formation of a solder bridge is avoided increases the reliability of the mechanical fastening of the electro-optical components and improves the high-frequency properties.
The second of the electro-optical components is especially preferably arranged on a front side of the printed circuit board facing the optics carrier. If the adjustment of the second of the electro-optical components is accomplished via the printed circuit board, direct access to the electro-optical component is not required and the second of the electro-optical components is able to be protected from a direct impact of force by the arrangement on the front side.
An alternative preferred embodiment provides that during the adjustment of the measuring device, the second of the electro-optical components is adjustable relative to the printed circuit board in the plane perpendicular to the associated optical axis of the second of the electro-optical components and the printed circuit board acts as a locating surface for the second of the electro-optical components in the direction of the associated optical axis of the second of the electro-optical components. The rear side of the printed circuit board establishes the position of the second of the electro-optical components in the direction of the associated optical axis and the electro-optical component is pressed against the printed circuit board during soldering so that a solder bridge is avoided.
The second of the electro-optical components is preferably arranged on a rear side of the printed circuit board facing away from the optics carrier. Due to the arrangement on the rear side of the printed circuit board, the second of the electro-optical components is accessible to a manipulator for positioning the second of the electro-optical components and for creating a soldered connection. In addition, the advantage of the arrangement on the rear side is that the printed circuit board, which is made of an insulating material, acts as a shield between the first and the second of the electro-optical components so that optical and electrical crosstalk between the electro-optical components is reduced.
The optics carrier is designed to be monolithic in a preferred embodiment. A monolithic optics carrier is made of one material and is not assembled from several individual parts. Monolithic optics carriers do not have a connecting zone between a first and second connection partner. The advantage of a monolithic optics carrier as compared to a multi-part optics carrier is that the optics carrier changes uniformly under the influence of temperature; there are no regions in the optics carrier that change in a different way as a function of temperature because of different material properties. Monolithic optics carriers have a high level of stability, thereby guaranteeing low adjustment tolerances and a high level of adjustment accuracy of the installed components.
The optics carrier is preferably designed of a metallic material, for example zinc. Metallic optics carriers produce an electrical shield between the electro-optical components and reduce electrical crosstalk between a beam source and a detector. Zinc is able to be processed in a die casting process with a high degree of precision and also possesses a high degree of temperature stability so that fluctuations in temperature to which laser distance measuring systems are frequently subjected only have a slight effect on the adjustment state of the installed components and the measuring properties of the measuring device.
The connecting device, which connects the first contact surface of the optics carrier to the second contact surface of the printed circuit board, is preferably designed as a screwed connection. Due to the screwed connection, a conductive connection is produced between the optics carrier and the printed circuit board. This is necessary in order to guarantee a good signal intensity, good EMC properties and a good shielding effect on the installed components.
Alternatively, the connecting device, which connects the first contact surface of the optics carrier to the second contact surface of the printed circuit board, is designed as an adhesive and screwed connection. The advantages of both connection techniques are combined in the case of an adhesive and screwed connection. With adhesion, the force is transferred two-dimensionally from one connection partner to the other. However, the adhesive connection may change under the influence of temperature. Brittleness may develop at low temperatures and the adhesive connection might soften at high temperatures. With a screwed connection, voltage peaks develop at the connection partners, while the space in between hardly contributes to the transmission of power. It is advantageous that screwed connections are only subject to a low influence of temperature.
Exemplary embodiments of the invention are described in the following on the basis of the drawings. These drawings are not necessarily supposed to represent the exemplary embodiments to scale, rather the drawings are executed in a schematic and/or slightly distorted form when this is useful for explanatory purposes. Reference is made to the pertinent prior art with respect to additions to the teachings directly identifiable from the drawings. It must be taken into consideration in this case that a wide range of modifications and changes related to the form and detail of an embodiment may be undertaken without deviating from the general idea of the invention. The features of the invention disclosed in the description, the drawings as well as in the claims may be essential for the further development of the invention both separately as well as in any combination. Moreover, all combinations of at least two features disclosed in the description, the drawings and/or the claims fall within the scope of the invention. The general idea of the invention is not restricted to the exact form or detail of the preferred embodiment described and depicted in the following or restricted to a subject matter which would be limited as compared to the subject matter claimed in the claims. In the case of any dimensioning ranges given, values within the stated limits are also meant to be disclosed as limit values, and be applicable at will and claimable. For the sake of simplicity, the same reference numbers are used in the following for identical or similar parts having an identical or similar function.